Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved magnetic read/write heads, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
FIG. 1 illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102, each equipped with a module 104. The bases are typically “U-beams” that are adhesively coupled together. Each module 104 includes a substrate 104A and a closure 104B with readers and writers 106 situated therebetween. In use, a tape 108 is moved over the modules 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in close proximity with the readers and writers 106.
Two common parameters are associated with heads of such design. One parameter includes the tape wrap angles αi, αo defined between the tape 108 and a plane 111 in which the upper surface of the tape bearing surface 109 resides. It should be noted that the tape wrap angles αi, αo includes an inner wrap angle αi which is often similar in degree to an external, or outer, wrap angle αo. The tape bearing surfaces 109 of the modules 104 are set at a predetermined angle from each other such that the desired inner wrap angle αi is achieved at the facing edges. Moreover, a tape bearing surface length 112 is defined as the distance (in the direction of tape travel) between edges of the tape bearing surface 109. The wrap angles αi, αo and tape bearing surface length 112 are often adjusted to deal with various operational aspects of heads such as that of Prior Art FIG. 1, in a manner that will soon become apparent.
During use of the head of FIG. 1, various effects traditionally occur. FIG. 2 is an enlarged view of the area encircled in FIG. 1. FIG. 2 illustrates a first known effect associated with the use of the head 100 of FIG. 1. When the tape 108 moves across the head as shown, air is skived from below the tape 108 by a skiving edge 204 of the substrate 104A, and instead of the tape 108 lifting from the tape bearing surface 109 of the module (as intuitively it should), the reduced air pressure in the area between the tape 108 and the tape bearing surface 109 allows atmospheric pressure to urge the tape towards the tape bearing surface 109.
As data density increases, gap-to-gap distance between the modules (gaps being where the elements are located) becomes more important. For example, in read-while-write operation, the readers on the trailing module read the data that was just written by the leading module so that the system can verify that the data was written correctly. If the data is not written correctly, the system will recognize the error and can rewrite the data. However, the tape does not move across the tape bearing surfaces perfectly linearly. Rather, the tape may shift back and forth, or “wobble,” as it crosses the tape bearing surfaces, resulting in dynamic skew, or misalignment of the trailing readers with the leading writers. The effects of wobble are exacerbated as track density increases. The farther the readers are behind the writers, the more chance that track misregistration will occur. If it does occur, the system may incorrectly believe that a write error has occurred. Additionally, there is an ongoing need to increase the number of active channels in the head for maintaining data rate as the number of tracks on the tape and thus cartridge capacity increases. For instance, a jump from 16 to 32 channels results in double the wiring, and so requires cabling comprising more than 128 leads, for modules with a reader/writer pair for each of the 32 channels plus servo readers and other connections. Such cabling is complex and bulky.
Further, a typical substrate to closure gap length is 25-35 microns for a piggyback reader/writer pair. The tape irregularities tend to droop slightly into this gap and erode the elements. This produces head-tape spacing problems, such as declining signal resolution.
There is accordingly a clearly-felt need in the art for a tape head assembly in which the gap-to-gap spacing between opposing modules is minimized. There is also a need for a tape head assembly that minimizes the substrate-to-closure gap length. There is a further need for a tape head assembly that allows the use of cables having a minimum number of I/O wires. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.